Optical modulation element and projection display device

ABSTRACT

Liquid crystal modulation elements  925 R,  925 G and  925 B are arranged so that light outgoing surfaces  9252 R,  9252 G and  9252 B thereof face light incident surfaces  911 R,  911 G and  911   b  of a color synthesizing prism  910 . Transparent plates  970 R,  970 G and  970 B are bonded to the light outgoing surfaces  9252 R,  9252 G and  9252 B of the liquid crystal modulation elements  925 R,  925 G, and  925 B. For this reason, adhesion of dust to the light outgoing surfaces  9252 R,  9252 G and  9252 B of the liquid crystal modulation elements  925 R,  925 G and  925 B can be prevented. Further, it is possible to prevent light reflection at the interface surface between the light outgoing surfaces  9252 R,  9252 G and  9252 B and air due to the difference in refractive index therebetween. This allows a high-quality image to be projected without deteriorating the switching characteristic of the liquid crystal modulation elements  925 R,  925 G and  925 B while preventing dirt from adhering to the light outgoing surfaces  9252 R,  9252 G and  9252 B of the liquid crystal modulation elements  925 R,  925 G and  925 B.

TECHNICAL FIELD

[0001] The present invention relates to an optical modulation elementand a projection display device. More particularly, the presentinvention relates to a layout structure of optical elements on theperiphery of an optical modulation element that modulates a light fluxaccording to image information.

BACKGROUND ART

[0002] A projection display device basically consists of a light sourcelamp unit, an optical unit for optically processing a light flux emittedfrom the light source lamp unit so as to synthesize a color imagecorresponding to image information, a projection lens unit for enlargingand projecting the synthesized light flux onto a screen, a power supplyunit, and a circuit substrate on which a control circuit and the likeare mounted.

[0003]FIG. 17 schematically shows the construction of the optical unitand the projection lens unit of the above-mentioned components. As shownin this drawing, an optical system of an optical unit 9 a includes alamp body 81 serving as a light source, a color separation opticalsystem 924 for separating a light flux W emitted from the lamp body 81into respective color light fluxes R, G and B of the primary colors ofred (R), green (G) and blue (B), three sheets of liquid crystalmodulation elements 925R, 925G and 925B for modulating the separatedrespective color light fluxes according to image information, and acolor synthesizing prism 910 in the shape of a prism with a square crosssection to synthesize the modulated color light fluxes. The light flux Wemitted from the lamp body 81 is separated into respective color lightfluxes R, G and B by the color separation optical system 924 includingvarious types of dichroic mirrors, and the red and green light fluxes Rand G of the respective color light fluxes are emitted from outgoingsections provided in the color separation optical system 924 towardscorresponding liquid crystal modulation elements 925R and 925G. The bluelight flux B is guided to the corresponding liquid crystal modulationelement 925B via a light guide system 927, and is emitted from anoutgoing section provided in the light guide system 927 towards thecorresponding liquid crystal modulation element 925B.

[0004] As shown in FIGS. 17(B) and 17(C) in enlargement, in the opticalunit 9 a, polarizers 960R, 960G and 960B are respectively arranged onthe side of incident surfaces of the liquid crystal modulation elements925R, 925G and 925B so that they unify the planes of polarization of therespective color light fluxes to be incident on the liquid crystalmodulation elements 925R, 925G and 925B. In addition, polarizers 961R,961G and 961B are respectively arranged on the side of outgoing surfacesof the liquid crystal modulation elements 925R, 925G and 925B so thatthey unify the planes of polarization of the modulated color fluxes tobe incident on the color synthesizing prism 910. The actions of thesepolarizers allow an enlarged image excellent in contrast to be projectedonto the surface of a screen 10. Of the two polarizers that sandwich theliquid crystal modulation elements 925R, 925G and 925B, the polarizers961R, 961G and 961B positioned on the side of the outgoing surfaces ofthe liquid crystal modulation elements 925R, 925G and 925B are bonded tothe light outgoing surfaces of the liquid crystal modulation elements.

[0005] Incidentally, as the liquid crystal modulation elements 925R,925G and 925B, an active matrix-type liquid crystal device is generallyused, in which pixels arranged in the form of a matrix are controlled bya switching element.

[0006] Here, in order to improve the contrast of an image enlarged andprojected onto the screen 10, it is effective to bond a polarizer, whichhas high selection properties with respect to polarized light, to thelight outgoing surface of each of the liquid crystal modulation elements925R, 925G and 925B. However, such a polarizer having high selectionproperties absorbs much light and therefore, generates much heat. Insidethe projection display device mentioned above, an air flow is formed asshown in FIG. 17(C) and cools the polarizer. However, since thepolarizer is directly attached to the light outgoing surface of theliquid crystal modulation element, heat is apt to be transmitted to theliquid crystal modulation element, and to thereby increase thetemperature of the liquid crystal modulation element. This increase intemperature deteriorates the optical properties of a liquid crystalpanel, and the image contrast.

[0007] Thus, it may be possible to arrange the polarizer apart from thelight outgoing surface of the liquid crystal modulation element.However, if the polarizer is simply arranged apart from the lightoutgoing surface, there is a fear that the switching element in theliquid crystal modulation element may malfunction due to a light beamreflected by the light outgoing surface of the liquid crystal modulationelement. In addition, there is a fear that dust or the like may becaused by an air flow formed inside the projection display device toadhere to the light outgoing surface of the liquid crystal modulationelement, and it may make high-quality image projection impossible.

[0008] In view of the above-described points, an object of the presentinvention is to provide an optical modulation element and a projectiondisplay device that achieve high-quality image projection by preventingdust from adhering to the light outgoing surface of the opticalmodulation element without deteriorating the switching characteristic ofthe optical modulation element.

DISCLOSURE OF INVENTION

[0009] In order to achieve the above-described object, there is providedan optical modulation element for modulating a light flux emitted from alight source according to image information, wherein a transparent plateis provided on at least one surface thereof, and the space between thetransparent plate and the optical modulation element is shielded fromthe outside by a dust-preventing member.

[0010] In such an optical modulation element, heat generated by apolarizer to be transmitted to the optical modulation element can befurther reduced. In addition, since the space between the transparentplate and the optical modulation element is shielded from the outside bythe dust-preventing member, dust does not enter the space. For thisreason, negative effects, such as the light flux emitted from theoptical modulation element being scattered by dust, can be solved.

[0011] The dust-preventing member may preferably be formed of resincontaining glass fiber. In this case, it is possible to restrict linearexpansion, to prevent movement of the optical modulation element, and tomaintain a constant temperature and a uniform in-plane temperaturedistribution of the optical modulation element.

[0012] On the other hand, the dust-preventing member may be made ofmetal. This makes it possible to improve the heat dissipation effect. Inparticular, when a polarizer is bonded to the transparent plate, it ispreferable that the dust-preventing member be made of metal because heatis generated with the absorption of light by the polarizer.

[0013] In the optical modulation element of the present invention, it isalso possible to bond the polarizer to the transparent plate. Thisprevents dust from entering between the polarizer and the transparentplate. For this reason, negative effects, such as the light flux emittedfrom the optical modulation element being scattered by dust, can beprevented more effectively.

[0014] In addition, in the optical modulation element of the presentinvention, at least one surface of the transparent plate may preferablybe coated with a surface-active agent, or treated for electrostaticprotection. This makes it possible to prevent dust from adhering to thetransparent plate.

[0015] A projection display device of the present invention may beconstructed in which a transparent plate is provided on the side of alight outgoing surface of the optical modulation element, and the spacebetween the transparent plate and the light outgoing surface of theoptical modulation element is shielded from the outside by adust-preventing member.

[0016] When the polarizer is arranged on the side of the light outgoingsurface of the transparent plate, since the transparent plate and an airlayer exist between the optical modulation element and the polarizer,heat generated by a polarizer to be transmitted to the opticalmodulation element can be further reduced. In addition, since the spacebetween the transparent plate and the optical modulation element isshielded from the outside by the dust-preventing member, dust does notenter the space. For this reason, bad effects, such as the light fluxemitted from the optical modulation element being scattered by dust, canbe solved.

[0017] As the dust-preventing member, a member having a frame body forholding the optical modulation element and the transparent plate, and alight outgoing-side outer frame detachably fixed to the light outgoingside of the frame body may be used. In the case of using such adust-preventing member, the frame body may be provided with a lightincident contact surface which contacts a part of the light incidentsurface of the optical modulation element, an optical modulation elementside contact surface which contacts the side surface of the opticalmodulation element, and a transparent plate side contact surface whichcontacts the side surface of the transparent plate. In addition, thelight outgoing-side outer frame may be provided with a pressure surfacethat can press a part of the light outgoing surface of the transparentplate towards the frame body.

[0018] This allows the optical modulation element to come into contactwith the light incident contact surface and the optical modulationelement contact surface provided on the frame body, thereby beingarranged in a predetermined position on the frame body. In addition, theposition of the transparent plate relative to the frame body and theoptical modulation element is defined by the the transparent platecontact surface and a spacer provided on the frame body. Therefore, ifthe light outgoing-side outer frame, is fixed to the frame body afterthe optical modulation element, spacer and transparent plate have beensuperposed in this order, the light outgoing surface of the transparentplate is pressed by the pressure surface of the light outgoing-sideouter frame towards the frame body side, so that the optical modulationelement, spacer and transparent plate can be held by the frame body andthe light outgoing-side outer frame, and at the same time, arrangementthereof in relation to one another can be maintained.

[0019] If the optical modulation element, the transparent plate and thelike are fixed to the frame body using an adhesive, replacement thereofrequires much labor. For example, after the optical modulation elementand the transparent plate are separated from the frame body, a step ofcleaning the adhesive adhering thereto is required.

[0020] In contrast, if the dust-preventing member such as describedabove is used, the light outgoing-side outer frame may merely be removedat the time of replacement of components, so that operability of reworkcan be improved.

[0021] It is desirable that a guide surface for putting a roller on thelight outgoing surface of the optical modulation element and moving theroller in one direction is provided on the frame body. An antireflectionfilm (AR film) may be bonded to the light outgoing surface of theoptical modulation element for the purpose of improving the lightutilizing efficiency. In such a case, if the roller is moved along theguide surface with the AR film placed on the light outgoing surface ofthe optical modulation element, the AR film can be easily bonded to thelight outgoing surface of the optical modulation element.

[0022] In addition, since the guide surface is formed and the roller canbe easily moved, it is easy to eliminate air bubbles generated betweenthe light outgoing surface of the optical modulation element and the ARfilm. When replacing the AR film to which dust is adhered, the lightoutgoing-side outer frame is removed from the frame body and thetransparent plate and the spacer are removed from the frame body.Thereafter, the AR film to which dust is adhered is separated from thelight outgoing surface of the optical modulation element, and a new ARfilm is bonded with the use of the guide surface as described abovewhile moving the roller. After the renewal of the AR film, the spacerand the transparent plate are superposed on the optical modulationelement and the light outgoing-side outer frame is fixed to the framebody. The AR film can be easily renewed by using the dust-preventingmember having the frame body on which the guide surface is formed.

[0023] In such a projection display device of the present invention, atleast one surface of the transparent plate may be coated with anantireflection film, whereby light reflected from the transparent plateto the optical modulation element can be eliminated as described above,and switching characteristic of the optical modulation element can bemaintained more excellently.

[0024] As the optical modulation element, either of transmissive orreflective optical modulation element may be used. When the transmissiveoptical modulation element is used, the transparent plate (lightincident-side transparent plate) may desirably be provided not only onthe side of the light outgoing surface, but also on the side of thelight incident surface thereof and further, the space between thetransparent plate provided on the side of the light incident surface andthe light incident surface of the optical modulation element maydesirably be shielded from the outside by the dust-preventing member.

[0025] When the transmissive optical modulation element is used and thetransparent plate is provided on the side of the light incident surfacethereof, a bonded light outgoing surface contacting a part of the lightoutgoing surface of the transparent plate on the side of the lightincident surface and a transparent side contact surface contacting theside surface of the light incident-side transparent plate may beprovided on the frame body of the dust-preventing member. In addition, alight incident-side outer frame detachably fixed to the light incidentside of the frame body may be provided, and a pressure surface that canpress the light incident surface of the light incident-side transparentplate towards the frame body may be provided on the light incident-sideouter frame. This allows the light incident-side transparent plate to beheld on the side of the light incident surface of the optical modulationelement without using an adhesive. In addition, the transparent platecan be easily replaced by only removing the light incident-side outerframe from the frame body.

[0026] When the light incident-side outer frame and the lightoutgoing-side outer frame are formed of the same shape, engaging pawlsextending along the side surface of the frame body are formed on therespective outer frames, and engaging projections each corresponding tothe engaging pawls are formed on the frame body, the positions of therespective engaging projections formed on the frame body may desirablybe shifted in the direction perpendicular to the thickness direction ofthe frame body. It is difficult to form a frame body on which thepositions of the respective engaging projections match in the thicknessdirection of the frame body by upper and lower dies. However, the framebody can be easily formed as in a conventional manner by using the framebody as described above. In addition, since the light incident-sideouter frame and the light outgoing-side outer frame have the same shape,commonality of components can be achieved.

[0027] The dust-preventing member may preferably be formed of resincontaining glass fiber. In this case, it is possible to restrict linearexpansion, to prevent movement of the optical modulation element, and tomaintain a constant temperature and a uniform in-plane temperaturedistribution of the optical modulation element.

[0028] On the other hand, if the dust-preventing member is made ofmetal, it is possible to improve the heat dissipation effect. Inparticular, when a polarizer is bonded to the transparent plate, it ispreferable that a mounting frame plate be made of metal because heat isgenerated with the absorption of light by the polarizer.

[0029] In the above-described projection display device of the presentinvention, it is also possible to bond the polarizer to the transparentplate. This prevents dust from entering between the polarizer and thetransparent plate. For this reason, negative effects, such as the lightflux emitted from the optical modulation element being scattered bydust, can be prevented more effectively.

[0030] In addition, in the above-described projection display device ofthe present invention, at least one surface of the transparent plate maypreferably be coated with a surface-active agent, or treated forelectrostatic protection. This makes it possible to prevent dust fromadhering to the transparent plate.

[0031] Furthermore, the projection display device of the presentinvention adopts a construction such as a projection display device forseparating a light flux emitted from a light source into a plurality ofcolor light fluxes, modulating respective color light fluxes accordingto image information through an optical modulation element, synthesizingrespective color light fluxes modulated by the optical modulationelement by a color synthesizing means, and enlarging and projectinglight synthesized by the color synthesizing means onto a projectionsurface through projection means, the projection display deviceincluding: a transparent plate provided on the side of a light outgoingsurface of the optical modulation element, a dust-preventing member forholding the transparent plate and the optical modulation element and forshielding the space between the transparent plate and the light outgoingsurface of the optical modulation element from the outside, a fixedframe plate fixed on the light incident surface of the colorsynthesizing means, and an intermediate frame plate removably fixed tothe fixed frame plate, wherein the dust-preventing member is fixed tothe intermediate frame plate. By the projection display device havingthis construction, the heat generated by the polarizer to be transmittedto the optical modulation element can be further reduced, and badeffects such that the light flux emitted from the optical modulationelement is scattered by dust can be avoided. In addition to this, sinceit is not necessary to mount the optical modulation element to the colorsynthesizing means side by directly touching the optical modulationelement, it is also possible to prevent the optical modulation elementfrom interfering with other parts and to prevent it from being broken orchipped.

[0032] In the projection display device of the present invention havingthis construction, it is convenient to provide positioning means forpositioning the optical modulation element by defining the mountingposition of the dust-preventing member because the mounting positions ofthe dust-preventing member and the optical modulation element can bedefined at the same time by this positioning means.

[0033] In the projection display device having this construction, whenthe transmissive optical modulation element is used, it is desirable toprovide the transparent plate not only on the side of the light outgoingsurface but also on the side of the light incident surface, as mentionedabove. It is also desirable that the space between the transparent plateprovided on the light incident surface side and the light incidentsurface of the optical modulation element is shielded from the outsideby the dust-preventing member.

[0034] Here, there may be a case where the polarizer is fixed to thelight incident surface of the color synthesizing means. In such a case,if the peripheral portion of the polarizer is completely superposed onthe bonded surface of the fixed frame plate, there is a fear that thebonding strength decreases or the polarizer is separated. In order toassuredly avoid such a problem, it may be preferable to form the fixedframe plate so that only a part of the bonded surface is superposed onthe peripheral portion of the polarizer. That is, it may be preferablethat the bonded surface of the fixed frame plate to the light incidentsurface is not completely covered with the polarizer.

[0035] The surface of the transparent plate may be coated with asurface-active agent, or treated for electrostatic protection. In thiscase, it is difficult for dust to adhere to the surface of thetransparent plate, and it is possible to prevent dust from adheringeffectively.

[0036] When a polarizer is bonded to the transparent plate, since it ispossible to prevent dust from entering between the optical modulationelement and the polarizer, the polarization condition of light is notdisturbed by dust. In addition, when a black image is displayed, a spoton the black image corresponding to the adhering dust can be preventedfrom being displayed as a white blank, and display quality can beimproved.

[0037] When the above-described dust-preventing member is formed ofresin containing glass fiber, it is possible to restrict linearexpansion, to prevent moving of the optical modulation element, and tomaintain a constant temperature and a uniform in-plane temperaturedistribution of the optical modulation element.

[0038] On the other hand, if the dust-preventing member is made ofmetal, it is possible to improve the heat dissipation effect. Inparticular, when a polarizer is bonded to the transparent plate, it ispreferable that the dust-preventing member be made of metal because heatis generated with the absorption of light by the polarizer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a perspective view showing an external shape of aprojection display device to which the present invention is applied.

[0040]FIG. 2 is a schematic plan structural view showing the internalconstruction of the projection display device shown in FIG. 1.

[0041]FIG. 3 is a schematic sectional structural view taken along theline A-A of FIG. 2.

[0042]FIG. 4 is a schematic plan structural view showing only an opticalunit and a projection lens unit.

[0043]FIG. 5 is a schematic structural view showing an optical systemincorporated into the optical unit.

[0044]FIG. 6 is an enlarged view of the surroundings of a liquid crystalmodulation element of a projection display device according to anembodiment 1 of the present invention.

[0045]FIG. 7 is a schematic sectional structural view of adust-preventing member.

[0046]FIG. 8 is a schematic plan structural view of the dust-preventingmember when viewed from the light incident side.

[0047]FIG. 9 is a schematic plan structural view of the dust-preventingmember when viewed from the light outgoing side.

[0048]FIG. 10(A) is an exploded perspective view showing a state inwhich the dust-preventing member is attached to a light incident surfaceof a color synthesizing prism, and

[0049]FIG. 10(B) is an illustration showing a large and smallrelationship between a fixed frame plate and a polarizer.

[0050]FIG. 11 is an exploded perspective view of an example of adust-preventing member different from the dust-preventing member shownin FIG. 7.

[0051]FIG. 12(A) is a schematic sectional structural view of thedust-preventing member shown in FIG. 11 when cut along an XZ plane, and

[0052]FIG. 12(B) is a schematic sectional structural view of thedust-preventing member shown in FIG. 11 when cut by a YZ plane.

[0053]FIG. 13 is an illustration showing a state in which a roller moveson a light outgoing surface of a liquid crystal modulation element.

[0054]FIG. 14 is a plan view showing the engagement between engagingpawls and engaging projections.

[0055]FIG. 15 is an exploded perspective view showing a state in whichthe dust-preventing member shown in FIG. 11 is attached to the colorsynthesizing prism.

[0056]FIG. 16 is a schematic structural view of the surroundings of aliquid crystal modulation element of a projection display deviceaccording to an embodiment 2 of the present invention.

[0057]FIG. 17 is a schematic structural view of an optical systemincorporated into an optical unit of a conventional projection displaydevice.

BEST MODE FOR CARRYING OUT THE INVENTION

[0058] <Embodiment 1>

[0059] An example of a projection display device to which the presentinvention is applied will be described below with reference to thedrawings. The projection display device of this embodiment separates alight flux emitted from a light source lamp unit into light fluxes ofthree primary colors of red (R), green (G) and blue (B), and these colorlight fluxes are modulated in correspondence to image informationthrough liquid crystal modulation elements, and modulated light fluxesof respective colors are synthesized and displayed in enlargement onto ascreen through a projection lens unit.

[0060]FIG. 1 shows an external appearance of the projection displaydevice of this embodiment. As shown in FIG. 1, a projection displaydevice 1 of this embodiment has an outer casing 2 in the shape of arectangular parallelepiped. The outer casing 2 basically consists of anupper casing 3, a lower casing 4 and a front casing 5 for defining thefront of the device. The leading end of a projection lens unit 6protrudes from the center of the front casing 5.

[0061]FIG. 2 shows the respective arrangement of components inside theouter casing 2 of the projection display device 1, and FIG. 3 shows across section taken along the line A A of FIG. 2. As shown in thesedrawings, inside the outer casing 2, a power supply unit 7 is arrangedon the rear end of the inside of the outer casing 2. A light source lampunit 8 is arranged at position adjacent to and offset from the powersupply unit 7 towards the front side of the device. An optical unit 9 isarranged in front of the light source lamp unit 8. A base end of theprojection unit 6 is positioned at the front center of the optical unit9.

[0062] On the other hand, an interface substrate 11 having aninput-output interface circuit mounted thereon is arranged on a side ofthe optical unit 9 so that it extends towards the front and reardirections of the device, and a video substrate 12 having a video signalprocessing circuit mounted thereon is arranged in parallel to therewith.Furthermore, a control substrate 13 for controlling the drive of thedevice is arranged above the light source lamp unit 8 and the opticalunit 9. Speakers 14R and 14L are arranged at the right and left frontcorners of the device, respectively.

[0063] A suction fan 15A for cooling is arranged on the center upperside of the optical unit 9, and a circulating fan 15B for forming acirculating stream for cooling is arranged on the center bottom side ofthe optical unit 9. In addition, an exhaust fan 16 is arranged on a sideof the device, which is the rear side of the light source lamp unit 8.Furthermore, an auxiliary cooling fan 17 for sucking a cooling airstream from the suction fan 15A into the power supply unit 7 is arrangedat a position in the power supply unit 7 opposed to the ends of thesubstrates 11 and 12.

[0064] A floppy-disk drive unit 18 is arranged directly above the powersupply unit 7 on the left side of the device.

[0065] The light source lamp unit 8 includes a light source lamp 80, anda lamp housing 83 containing therein the light source lamp 80. The lightsource lamp 80 includes a lamp body 81 such as a halogen lamp, a xenonlamp, or a metal halide lamp, and a reflector 82 including a reflectingsurface that is parabolic in cross section, and it can reflect divergentlight from the lamp body 81 so that the light emerges towards theoptical unit 9 almost along an optical axis.

[0066]FIG. 4 shows only the optical unit 9 and the projection lens unit6. As shown in this drawing, in the optical unit 9, optical elementsother than a color synthesizing prism 910 are vertically sandwiched andheld between the upper and lower light guides 901 and 902. The upperlight guide 901 and the lower light guide 902 are fixed by fixing screwson the sides of the upper casing 3 and the lower casing 4, respectively.

[0067] In addition, these upper and lower light guide plates 901 and 902are similarly fixed on the sides of the color synthesizing prism 910 byfixing screws. The color synthesizing prism 910 is fixed by fixingscrews on the rear of a thick head plate 903 formed of a die-castingplate. The base end of the projection lens unit 6 is similarly fixed onthe front of the head plate 903 by fixing screws.

[0068]FIG. 5 shows a schematic construction of an optical systemincorporated into the projection display device 1 of this embodiment.The optical system in the projection display device 1 of this embodimentadopts a light source lamp 80, which is a component of the light sourcelamp unit 8, and a uniform illumination optical system 923 consisting ofintegrator lenses 921 and 922, which are uniform illumination opticalelements. The projection display device 1 includes a color separationoptical system 924 for separating a light flux W emitted form theuniform illumination optical system 923 into red (R), green (G) and blue(B), three sheets of liquid crystal modulation elements 925R, 925G and925B for modulating the respective color light fluxes R, G and B, thecolor synthesizing prism 910 serving as a color synthesizing opticalsystem for synthesizing the modulated color light fluxes, and a lightguide system 927 for guiding the synthesized light fluxes to the liquidcrystal modulation element 925B corresponding to the blue light flux Bin the projection lens unit 6 that enlarges and projects the synthesizedcolor light fluxes onto the surface of the screen 10.

[0069] The uniform illumination optical system 923 includes a reflectingmirror 931 so as to bend an optical axis 1 a of outgoing light from theuniform illumination optical system 923 at the right angle towards thefront of the device. The integrator lenses 921 and 922 are arranged inthe state of being perpendicular to each other with this reflectingmirror 931 sandwiched therebetween.

[0070] Light emitted from the light source lamp 80 is projected as asecondary source image through the integrator lens 921 onto the incidentsurface of each of the lenses constituting the integrator lens 922, sothat an object to be illuminated is irradiated using the outgoing lightfrom the integrator lens 922.

[0071] The color separation optical system 924 consists of a blue-greenreflecting dichroic mirror 941, a green reflecting dichroic mirror 942and a reflecting mirror 943. First, the blue light flux B and the greenlight flux G contained in the light flux W are reflected at right anglesby the blue-green reflecting dichroic mirror 941, and directed towardsthe green reflecting dichroic mirror 942.

[0072] The red light flux R passes through this mirror 941, and isreflected at right angles by the rear reflecting mirror 943 locatedbehind, and emitted from an outgoing section 944 for the red light fluxR to the side of the prism unit 910. Next, only green light flux G ofthe blue and green light fluxes B and G reflected by the mirror 941 isreflected at right angles by the green reflecting dichroic mirror 942,and is emitted from an outgoing section 945 for the green light flux Gto the side of the color synthesizing optical system. The blue lightflux B passing through this mirror 942 is emitted from an outgoingsection 946 for the blue light flux B to a side of the light guidesystem 927. In this embodiment, all the distances between the outgoingsection for the light flux W of the uniform illumination optical elementand the outgoing sections 944, 945 and 946 for the color light fluxes ofthe respective color separation optical system 924 are equally set.

[0073] Condenser lenses 951 and 952 are arranged on the outgoing sidesof the outgoing sections 944 and 945 of the red and green light fluxes Rand G in the color separation optical system 942, respectively.Therefore, the red and green light fluxes R and G emitted from theoutgoing sections respectively are incident on these condenser lenses951 and 952, where they are collimated.

[0074] The thus collimated red and green light fluxes R and G areincident on the liquid crystal modulation elements 925R and 925G to bemodulated, and given image information corresponding thereto. That is,these light valves are subjected to switching control by non-illustrateddriving means according to image information, whereby each color lightpassing therethrough is modulated. As such driving means, well-knownmeans may be used unchanged.

[0075] On the other hand, the blue light flux B is guided to thecorresponding liquid crystal modulation element 925B through the lightguide system 927, where it is similarly modulated according to the imageinformation. In the light valves of this embodiment, for example, apoly-silicon TFT may be used as a switching element.

[0076] The light guide system 927 consists of a condenser lens 954arranged on the outgoing side of the outgoing section 946 for the bluelight flux B, an incident-side reflecting mirror 971, an outgoing-sidereflecting mirror 972, an intermediate lens 973 arranged between thesereflecting mirrors, and a condenser lens 953 arranged upstream of theliquid crystal modulation element 925B. The blue light flux B of thecolor light fluxes has the longest optical path lengths, that is, thedistances between a light source lamp 805 and each of the liquid crystalpanels, and therefore, the amount of light of the blue light flux B tobe lost is the largest. However, the light loss can be restricted byinterposing the light guide system 927 therebetween.

[0077] Next, the respective color light fluxes R, G and B modulatedpassing through the respective liquid crystal modulation elements 925R,925G and 925B are incident on the color synthesizing prism 910, wherethey are synthesized. A color image synthesized by the colorsynthesizing prism 910 is enlarged and projected through the projectionlens unit 6 onto the surface of the screen 10 located at a predeterminedposition.

[0078]FIG. 6 schematically shows a construction of the surroundings ofthe liquid crystal modulation elements.

[0079] As shown in FIG. 6, in this embodiment, transparent plates 962R,962G, 962B, 963R, 963G and 963B made of plastic or glass are providedbetween dust-preventing members 965R, 965G and 965B on the side of thelight incident surfaces and on the side of the light outgoing surfacesof the liquid crystal modulation elements 925R, 925G and 925B,respectively, which are plane-opposed to light incident surfaces 911R,911G and 911B of the color synthesizing prism 910 at a predetermineddistance. Spaces between the transparent plates 962R, 962G, 962B, 963R,963G and 963B and the liquid crystal modulation elements 925R, 925G and925B are shielded from the outside by the dust-preventing members 965R,965B and 965B. For this reason, since dust does not enter between thetransparent plates 962R, 962G, 962B, 963R, 963G and 963B and the liquidcrystal modulation elements 925R, 925G and 925B, the respective colorlight fluxes can be prevented from being scattered by the dust. Inaddition, the light outgoing surfaces of the liquid crystal modulationelements 925R, 925G and 925B are coated with light antireflection thinfilms, thereby preventing the aforementioned malfunction of the liquidcrystal modulation elements 925R, 925G and 925B due to the return lightdescribed above.

[0080] The incident and outgoing surfaces of the transparent plates963R, 963G and 963B are also coated with light antireflection thinfilms.

[0081] Incident-side polarizers 960R, 960G and 960B are arranged at apredetermined distance from the light incident surfaces of thetransparent plates 962R, 962G and 962B, and outgoing-side polarizers961R, 961G and 961B are bonded to the light incident surfaces 911R, 911Gand 911B of the color synthesizing prism 910, respectively.

[0082] In the thus constructed projection display device, since theincident-side polarizers 960R, 960G and 960B and the outgoing-sidepolarizers 961R, 961G and 961B are provided apart from the lightincident surfaces and light outgoing surfaces of the liquid crystalmodulation elements 925R, 925G and 925B, and the transparent plates962R, 962G and 962B, 963R, 963G and 963B and air are provided betweenthe incident-side polarizers 960R, 960G and 960B, the outgoing-sidepolarizers 961R, 961G and 961B and the liquid crystal modulationelements 925R, 925G and 925B, it is possible to prevent heat generatedby the incident-side polarizers 960R, 960G and 960B and theoutgoing-side polarizers 961R, 961G and 961B from being transmitted tothe liquid crystal modulation elements 925R, 925G and 925B. In addition,since the light outgoing surfaces of the liquid crystal modulationelements 925R, 925G and 925B are protected by the transparent plates963R, 963G and 963B, and the transparent plates 963R, 963G and 963B areapart from the light outgoing surfaces of the liquid crystal modulationelements 925R, 925G and 925B, it is possible to prevent heat generatedby the outgoing-side polarizers 961R, 961G and 961B from beingtransmitted to the liquid crystal modulation elements 925R, 925G and925B. This makes it possible to restrict the increase in temperature ofthe liquid crystal modulation elements 925R, 925G and 925B and toprevent the deterioration of optical properties thereof.

[0083] In addition, since the liquid crystal modulation elements 925R,925G and 925B and the outgoing-side polarizers 961R, 961G and 961B areapart from each other, the light emitted from the liquid crystalmodulation elements 925R, 925G and 925B is widely spread, and the lightcan be received by a wide area. For this reason, it is possible todecrease the heat generated by the polarizers 961R, 961G and 961B perunit area, and to permit easy heat dissipation. In particular, it iseffective to arrange a michrolens array, which gathers light onto eachpixel of the liquid crystal modulation elements, on the side of thelight incident surfaces of the liquid crystal modulation elements 925R,925G and 925B because the light can spread more widely.

[0084] Furthermore, in the projection display device of this embodiment,since the transparent plates 962R, 962G and 962B are bonded to the sideof the light incident surfaces of the liquid crystal modulation elements925R, 925G and 925B, it is possible to prevent dust from adhering to thelight incident surfaces of the liquid crystal modulation elements 925R,925G and 925B.

[0085] Incidentally, the outgoing-side polarizers 961R, 961G and 961Bmay surely be bonded to the transparent plates 963R, 963G and 963Bwithout being bonded to the light incident surfaces 911R, 911G and 911Bof the color synthesizing prism 910. In this case, it is possible toprevent dust from entering between the liquid crystal modulationelements 925R, 925G and 925B and the polarizers 961R, 961G and 961B, andto thereby prevent the polarization condition of light from beingdisturbed by dust. In addition, when a black image is displayed, itsportion corresponding to the adhering dust can be prevented from beingdisplayed as a white blank, and the display quality can be improved.

[0086] In addition, the outgoing-side polarizers 961R, 961G and 961B maysurely be independently arranged between the transparent plates 962R,962G, 962B and the color synthesizing prism 910.

[0087] Further, the surfaces of such transparent plates 962R, 962G,962B, 963R, 963G and 963B may be coated with a surface-active agent(surfactant), or treated for electrostatic protection. This makes itdifficult for dust to adhere to the surfaces of the transparent plates962R, 962G, 962B, 963R, 963G and 963B, so that adhesion of the dust canbe prevented more effectively.

[0088] Incidentally, the polarizers include two types of polarizers, areflective polarizer and an absorptive polarizer. The reflectivepolarizer transmits one of two types of linearly polarized light, andreflects the other linearly polarized light. In addition, the absorptivepolarizer transmits one of two types of linearly polarized light andabsorbs the other linearly polarized light. The polarizers 960R, 960G,960B, 961R, 961G and 961B may be either reflective or transmissive.

[0089] The structure of the dust-preventing members 965R, 965G and 965Bwill now be described in detail. Incidentally, since the respectivedust-preventing members 965R, 965G and 965B have the same construction,only the dust-preventing member 965R will be described on behalfthereof. In addition, in the following explanation, three directionsperpendicular to one another are referred to as the X-axis direction(lateral direction), the Y-axis direction (vertical direction) and theZ-axis direction (direction parallel to the optical axis) forconvenience. FIG. 7 shows a schematic sectional construction of thedust-preventing member 965R. In addition, FIG. 8 shows a schematic planconstruction of the dust-preventing member 965R when viewed from theside of the light incident surface, and FIG. 9 shows a schematic planconstruction when viewed from the side of the light outgoing surface.

[0090] As shown in these drawings, the transparent plate 962R isarranged on the light incident surface of the liquid crystal modulationelement 925R through a spacer 21, and the transparent plate 963R isarranged on the light outgoing surface through a spacer 22. In thisembodiment, the liquid crystal modulation element 925R, and transparentplates 962R and 963R are maintained in such an arrangement by thedust-preventing member 965R.

[0091] The dust-preventing member 965R includes first and second outerframes 51 and 52 for clamping the liquid crystal modulation element 925Rand transparent plates 962R and 963R, and an intermediate frame 53 forshielding the space between the light outgoing surface of the liquidcrystal modulation element 925R and the transparent plate 963R, and thespace between the light incident surface of the liquid crystalmodulation element 925R and the transparent plate 962R from the outside.The liquid crystal modulation element 925R, transparent plates 962R and963R are held between the first and second outer frames 51 and 52.

[0092] The first outer frame 51 includes a rectangular opening 51 a forlight transmission, and a peripheral wall 51 b having a uniformthickness on the periphery thereof. The second outer frame 52 alsoincludes a rectangular opening 52 a for light transmission, and aperipheral wall 52 b having a uniform thickness on the peripherythereof. The vertical (vertical direction Y) length of the second outerframe 52 is set longer than the transparent plate 963R, and shorter thanthe first outer frame 51.

[0093] The intermediate frame 53 is a rectangular frame, and is providedto surround the outer periphery of the liquid crystal modulation element925R, and transparent plates 962R and 963R. Engaging projections 53 aare formed at respective left and right positions on the side surface ofthis intermediate frame 53. In contrast, the engaging holes 51 lccapable of fitting therein these engaging projections 53 a are formed onthe side surface of the first outer frame 51 at positions correspondingto the engaging projections 53 a.

[0094] Engage projections 53 b are also formed at respective left andright positions on the side surface of this intermediate frame 53. Incontrast, the engaging holes 52 c capable of fitting in these engagingprojections 53 b are formed on the side surface of the second outerframe 52 at positions corresponding to the engaging projections 53 b.

[0095] Therefore, if the first outer frame 51 is pressed into theintermediate frame 53 so that each of the engaging projections 53 a areinserted into respective engaging holes 51 c from the outside of thetransparent plate 962R provided on the side of the light incidentsurface of the liquid crystal modulation element 925R, and if the secondouter frame 52 is pressed into the intermediate frame 53 so that each ofthe engaging projections 53 b are inserted into each of the engagingholes 52 c from the outside of the transparent plate 963R provided onthe side of the light outgoing surface of the liquid crystal modulationelement 925R, the liquid crystal modulation element 925R, thetransparent plates 962R and 963R are held by the dust-preventing member965R.

[0096] In addition, the space between the light incident surface of theliquid crystal modulation element 925R and the transparent plate 962R,and the space between the light outgoing surface of the liquid crystalmodulation element 925 R and the transparent plate 963R are shieldedfrom the outside. Incidentally, a flexible cable 9253R for wiringextends upward from the dust-preventing member 965R.

[0097] In this case, if the dust-preventing member 965R is made of resincontaining glass fiber, such as FRP, it is possible to restrict linearexpansion, to prevent the shift of the dust-preventing member 965R, andto maintain a constant temperature and a uniform in-plane temperature ofthe dust-preventing member 965R.

[0098] On the other hand, if the dust-preventing member is made ofmetal, it is possible to improve the heat dissipation effect. Inparticular, when light-absorptive polarizer is bonded to the transparentplate, the heat caused by light being absorbed by the polarizer can beefficiently radiated.

[0099]FIG. 10(A) illustrates a state in which the dust-preventing member965R holding the liquid crystal modulation element 925R, and thetransparent plates 962R and 963R is attached to the light incidentsurface 9llR of the color synthesizing prism 910. An attachmentstructure for attaching the dust-preventing member 965R to the lightincident surface 911R of the color synthesizing prism 910 will bedescribed with reference to this drawing.

[0100] As shown in FIG. 10(A), the dust-preventing member 965R holdingthe liquid crystal modulation element 925R and the like is fixed to afixed frame plate 54 to be fixedly bonded to the light incident surface911R of the color synthesizing prism 910. Incidentally, a red filter 23is bonded to the light incident surface 911R of the color synthesizingprism 910 of this embodiment, and the polarizer 961R is fixed to thesurface of the red filter 23.

[0101] An intermediate frame plate 55 is a rectangular frame that isformed in almost the same or a larger size of the first outer frame 51of the dust-preventing member 965R, and includes a rectangular opening55 a for light transmission. The intermediate frame plate 55 hasengaging projections 55 d that extend perpendicularly from the surfaceof the frame plate at the four corners of the rectangular opening 55 athereof. In contrast, the dust-preventing member 965R has engaging holes51 d formed at positions corresponding to the engaging projections 55 d,into which the engaging projections 55 d can be inserted.

[0102] In this embodiment, the engaging holes 51 d are formed by throughholes that are formed in the first outer frame 51 and the intermediateframe 53 of the dust-preventing member 965R. Therefore, when therespective engaging holes of the dust-preventing member 965R and therespective engaging projections of the intermediate frame plate 55 arealigned and overlaid one on another, the respective engaging projections55 d are inserted in the respective engaging holes 51 d, whereby atemporarily attached state is formed.

[0103] On the other hand, the fixed frame plate 54 is also a rectangularframe plate having a rectangular opening 54 a for light transmission. Inaddition, the rectangular opening 54 a formed in the fixed frame plate54 is formed smaller than the light incident surface of the polarizer961R. The fixed frame plate 54 is fixed to the red filter 23 provided onthe light incident surface 911R of the color synthesizing prism 910 withan adhesive.

[0104] At this time, if the bonded surface 54 e of the fixed frame plate54 is completely covered with the polarizer 961R, there is a fear thatthe bonding strength decreases and the polarizer 961R is separated. Inthis embodiment, however, as shown in FIG. 10(B), since the bondedsurface 54 e of the fixed frame plate 54 is not completely covered withthe polarizer 961R, there is an extremely little possibility of adecrease in bonding strength and separation of the polarizer 961R.

[0105] Returning to FIG. 10(A), the fixed frame plate 54 has screw holes54 c at both ends of its upper frame section and at the widthwise centerof its lower frame section. The intermediate frame plate 55 also hasscrew holes 55 c corresponding to the three screw holes 54 c. Byinserting flat-head screws 56 for fastening into the corresponding screwholes 54 c and 55 c, the intermediate frame plate 55 is fixed to thefixed frame plate 54. Incidentally, in this embodiment, the intermediateframe plate 55 is fixed to the fixed frame plate 54 by the three screws56. The number of screws is not limited and may be four or more, and twoor less. In general, as the number of screws decreases, the number ofsteps of fastening the screws decreases, and manufacturing isfacilitated.

[0106] Here, the fixed frame plate 54 has engaging projections 54 b atthe right and left corners of its lower frame section, and theintermediate frame plate 55 has engaging holes 55 b at the right andleft corners of its lower frame section corresponding to the twoengaging projections 54 b. Therefore, when being fixed with the screws56, the intermediate frame plate 55 can be temporarily fixed to thefixed frame plate 54 by pressing the intermediate frame plate 55 towardsthe fixed frame plate 54 while aligning the engaging holes 55 b of theintermediate frame plate 55 with the engaging projections 54 b of thefixed frame plate 54. This makes it possible to further improve thepositioning accuracy of both the frame plates.

[0107] The projection display device of this embodiment includespositioning means for positioning the dust-preventing member 965R to theintermediate frame plate 55 that is fixed to the fixed frame plate 54.This positioning means includes two wedges 57. Wedge guide surfaces 5leto 51 g, against which inclined surfaces 57 a of the wedges 57 abut, areformed on the vertical centers of the right and left side surfaces ofthe dust-preventing member 965R. When the dust-preventing member 965R istemporarily attached to the intermediate frame plate 55, wedge insertiongrooves are formed between the wedge guide surfaces 51 e and the framesections of the intermediate frame plate 55 facing the wedge guidesurfaces 51 e.

[0108] Therefore, after the dust-preventing member 965R has beentemporarily attached to the intermediate frame plate 55, the two wedges57 are struck in the right and left sides of the dust-preventing member965R, and the amount of the wedges 57 to be pressed in is adjusted,whereby the position of the dust-preventing member 965R is defined, andthe liquid crystal modulation element 925R held by the dust-preventingmember 965R can be positioned.

[0109] A description will now be given of a procedure of attaching thedust-preventing member 965R to the light incident surface 911R of thecolor synthesizing prism 910. First, the dust-preventing member 965R bywhich the liquid crystal modulation element 925R and the transparentplates 962R and 963R are held is prepared. In addition, the colorsynthesizing prism 910 having the light incident surface 911R to whichthe polarizer 961R is fixed through the red filter 23 is prepared. Next,the fixed frame plate 54 is positioned and fixedly bonded to the redfilter 23 that is fixed to the light incident surface 911R of the colorsynthesizing prism 910. An ultraviolet-curing adhesive or the like maybe used as an adhesive.

[0110] Then, the intermediate frame plate 55 is positioned on thesurface of the fixed frame plate 54 that is fixedly bonded, and theintermediate frame plate 55 is fastened by the three flat-head screws56. Thereafter, the dust-preventing member 965R by which the liquidcrystal modulation element 925R and the like are held is positioned onthe intermediate frame plate 55, and is temporarily attached thereto.That is, the engaging projection 55 d of the intermediate frame plate 55is aligned with the engaging hole 51 d of the dust-preventing member965R, and the dust-preventing member 965R is pressed towards theintermediate frame plate 55 in this state. Incidentally, if the fixedframe plate 54 and the intermediate frame plate 54 are combined inadvance by screws 56 before fixedly bonding the fixed frame plate 54 tothe color synthesizing prism 910, the accuracy of position can be easilyobtained.

[0111] Thereafter, the liquid crystal modulation element 925R ispositioned onto the light incident surface 911R of the colorsynthesizing prism 910 using the wedges 57 as the positioning means.That is, the two wedges 57 are inserted between the dust-preventingmember 965R and the intermediate frame plate 55 that are temporarilyattached, along the wedge guide surface 51 e formed on thedust-preventing member 965R. Then, the alignment and focusing of theliquid crystal modulation element 925R are adjusted by controlling theamount of insertion of the wedges 57.

[0112] When the positioning is completed, these wedges 57 are fixedlybonded with an adhesive to the dust-preventing member 965R and theintermediate frame plate 55 that are the members to be positioned. Asthe adhesive used in this case, an ultraviolet-curing adhesive can alsobe used.

[0113] The positioning operation and the fixedly bonding operation ofthe above wedges 57 will now be described in more detail following thesequence of steps.

[0114] First, a focal surface of the liquid crystal modulation element925R is adjusted into a focal surface of the projection lens unit 6using a specific adjustment device. In this state, as mentioned above,the ultraviolet-curing adhesive is filled into the gap formed when theengaging projection 55 d of the intermediate frame plate 55 is insertedinto the engaging hole 51 d of the dust-preventing member 965R, andcured by radiation of ultraviolet-ray to effect temporarily fixing.

[0115] Then, by the intermediate frame plate 55 and the wedge guidesurfaces 51 e provided on the dust-preventing member 965R, theultraviolet-curing adhesive is irradiated with ultraviolet-ray from theexposed end surfaces of the wedges 57 to effect bonding and actualfixing. Similarly, focusing and pixel-matching between the liquidcrystal modulation elements 925R and 925B are adjusted with reference tothe liquid crystal modulation element 925G that is arranged in thecenter of the liquid crystal modulation elements 925R, 925G and 925B soas to effect the temporarily fixing and the actual fixing.

[0116] Incidentally, since the temporarily fixing is effected by asetting adjustment device with the color synthesizing prism 910 and theprojection lens 6 attached to the head plate 903, it is possible toadjust optimally in accordance with characteristics of individualcomponents. In addition, the dust-preventing member 965R is chucked inthe adjustment device with reference to the external shape of the firstouter frame 51.

[0117] Since the attachment structure of the dust-preventing members965G and 965B holding the liquid crystal modulation elements 925G and925B other than the liquid crystal modulation element 925R to the colorsynthesizing prism 910 is the same as that of the dust-preventing member965R, a description thereof will be omitted.

[0118] When the dust-preventing member 965R is attached to the colorsynthesizing prism 910 as described above, the following effects can beobtained.

[0119] Firstly, since the peripheral portion of the liquid crystalmodulation element 925R is protected by the dust-preventing member 965R,it is not necessary to directly touch the liquid crystal modulationelement 925R so as to attach it to the color synthesizing prism 910.Therefore, it is possible to prevent the liquid crystal modulationelement 925R from abutting against other portions and to prevent it frombeing broken or chipped. In addition, since the surroundings of theliquid crystal modulation element 925R are covered with thedust-preventing member 965R, it is possible to cut off external light,and to prevent the malfunction of the liquid crystal modulation 925R dueto the external light.

[0120] Secondly, the dust-preventing member 965R holding the liquidcrystal modulation element 925R is detachably fastened by screws to thelight incident surface 911R of the color synthesizing prism 910 throughthe intermediate frame plate 55. Therefore, for example, when the liquidcrystal modulation element 925R becomes defective, it can be replaced bya simple operation of removing the screws 56. In addition, since theliquid crystal modulation element 925R is not directly fixedly bonded tothe color synthesizing prism 910, the color synthesizing prism 910 isnot damaged at the time of the replacement, and expensive components canbe used most efficiently.

[0121] Thirdly, the dust-preventing member 965R holding the liquidcrystal modulation element 925R can be temporarily attached to theintermediate frame plate 55. After forming this temporarily attachedstate, the liquid crystal modulation element 925R and the light incidentsurface 911R of the color synthesizing prism 910 can be positioned usingthe wedges 57. Since the temporarily attached state can be formed asdescribed above, the positioning operation using the wedges 57 can beeasily performed in a separate step, thus contributing to an improvementof the cycling time of the equipment.

[0122] In general, the wedges 57 made of glass can be used. However,when the dust-preventing member 965R is formed of resin, since it has ahigh thermal expansion coefficient as compared with glass, the wedges 57may tend to be separated from the frame plate due to the difference inthermal expansion, and may be broken by a change in temperature. Inorder to avoid these matters, it is desirable that the wedges 57 beformed of resin of the acrylic group or the like. In addition, thewedges 57 can be molded by being formed of an acrylic material, so thatthe cost thereof can be substantially reduced as compared with a glassmaterial. Incidentally, by using materials that transmit ultraviolet-rayas the material of the wedges 57, a ultraviolet-curing adhesive oflittle increase in temperature and of short curing time can be used asthe adhesive for fixedly bonding the wedges 57.

[0123] In addition, the wedge guide surfaces 51 e are formed on thedust-preventing member 965R, whereby the upper end surfaces 51 f and 51g are formed on upper and lower portions thereof, and the wedges 57 areguided by these three surfaces. That is, when the adhesive is filledinto the portions and the wedges 57 are inserted thereinto, the wedges57 are automatically moved to the inside while being guided by thesethree surfaces due to the surface tension of the adhesive. Therefore,the wedges 57 become resistant to disturbance encountered in steps, andcan be easily attached.

[0124] While the adhesive is used when the dust-preventing member 965Ris temporarily fixed to the intermediate frame plate 55, soldering orthe like may be used instead of the adhesive. When the dust-preventingmember 965R and the like are made of resin, a substance having ametallic member bonded to the joint thereof, or a substance having ametalized layer formed on the joint thereof may be used.

[0125] The above-described dust-preventing member 965R, intermediateframe plate 55 and fixed frame plate 54 can be formed of thermosettingresin into which glass fiber or calcium carbonate is mixed. When such aresin material is used, the thermal expansion coefficient thereofbecomes close to that of glass as compared with a common resin material.For this reason, pixel displacements and the like due to thermaldeformation can be avoided in the state where they are bonded to thecolor synthesizing prism 910.

[0126] While the ultraviolet-curing adhesive can be used as the adhesivefor fixedly bonding the fixed frame plate 54 to the color synthesizingprism 910 as described above, it may be desirably coated with abase-processing material in order to increase bonding properties. Thatis, in the color synthesizing prism 910, the incident surface 911R ofthe red light flux faces the incident surface 911B of the blue lightflux as described above. Since the blue light flux has a shortwavelength, a part thereof may be transmitted through a reflecting filmof the color synthesizing prism 910 to reach the opposite incidentsurface 911R of the red light flux. If such backlight is incident on theliquid crystal modulation element 925R, a malfunction may be caused. Inthis embodiment, since the red filter 23 is provided on the incidentsurface 911R of the red light flux, it is possible to cut off such abacklight, and to thereby prevent the malfunction of the liquid crystalmodulation element 925R due to the backlight.

[0127] The filter is attached only to the incident surface 911R of thered light flux because of the largest influence of the backlight of theblue light flux. This, however, does not apply to a case in which theinfluence of the backlight of other light fluxes is large. The filtermay be provided on another surface, or filters may be provided on aplurality of surfaces.

[0128] However, the presence of such a filter blocks ultraviolet rays atthe time of fixedly bonding, whereby a portion lacking inultraviolet-ray radiation is generated in the ultraviolet-curingadhesive for fixedly bonding the fixed frame plate 54 to the incidentsurfaces 911R, 911G and 911B of the color synthesizing prism 910. Inorder to avoid the negative effects so as to assuredly fixedly bond thefixed frame plate 54 to the incident surface 911R, it is desirable thatthese bonded surfaces are coated with the base-processing material andthat an anaerobic type adhesive is used together with theultraviolet-curing adhesive. Of course, the incident surface having nosuch filter may be treated for a similar process.

[0129] While the use of the ultraviolet-curing adhesive is describedabove, other adhesives may be used. For example, when a hot-melt typeadhesive is used to fixedly bond the fixed frame plate 54 and the wedges57, there is no need to consider the above problem arising from thefilter.

[0130] In addition, in this embodiment, the fixed frame plate 54 and theintermediate frame plate 55 are flat. As described with reference toFIG. 3, the fan 15B is arranged below the color synthesizing prism 910,and cooling air flows from bottom to top. In order to prevent this flowfrom being disturbed, it is desirable to arrange straightening vanesabove the fan 15B. Since the fixed frame plate 54 and the intermediateframe plate 5 are flat, the straightening vanes can be mounted at aposition directly below the liquid crystal modulation element 925R andhence, cooling air can flow effectively from bottom to top. Further,since these frame plates have a simple shape, parts can be easilyutilized, and the accuracy of the parts is thereby improved.

[0131] In addition to this, the two wedges 57 are used for positioning,and they are fixedly bonded to the vertical centers of the right andleft sides of the dust-preventing member 965R and the intermediate frameplate 55. If the wedges 57 are fixedly bonded at inadequate positions,there is a fear that excessive stress concentration is caused in thecomponents by thermal deformation of the dust-preventing member 965R,the intermediate frame plate 55, or the wedges 57. In addition, this maycause the wedges 57 to separate from the dust-preventing member 965R orthe intermediate frame plate 55.

[0132] As described above, however, since the wedges 57 are fixedlybonded to the centers of the right and left sides, the dust-preventingmember 965R and the intermediate frame plate 55 are free to thermallydeform in the vertical direction, centered on the wedges 57. Therefore,the degree to which the thermal deformation of these frame plates isrestrained is low, so that negative effects, such as undesired stressconcentration and separation of wedges, can be avoided.

[0133] Further, as apparent from FIG. 10(A), each of the wedges 57 inthis embodiment has two blind holes 57 c formed on its rear surface 57b. These blind holes 57 c, in chucking the wedges 57 with a jig,function as engaging portions for chucking. The formation of such blindholes 57 c permits easy chucking and therefore, handling thereof becomeseasy.

[0134] In this embodiment, the blind holes 57 c for engagement inchucking are formed on the rear side of the wedges 57. The engagingportions for chucking may be formed on other members. For example,engaging portions for chucking, such as blind holes, may be formed onthe outer surface of the dust-preventing member 965R.

[0135] A modification of the dust-preventing member 965R will now bedescribed. FIG. 11 is an exploded perspective view of a modification ofthe dust-preventing member 965R. FIG. 12(A) is a schematic sectionalstructural view of a dust-preventing member 1965R when cut along an XZplane, and FIG. 12(B) is a schematic sectional structural view of thedust-preventing member 1965R shown in FIG. 11 when cut along a YZ plane.

[0136] As shown in these drawings, the dust-preventing member 1965Rholds the liquid crystal modulation element 925R and the transparentplates 962R and 963R. The dust-preventing member 1965R has anintermediate frame 30, a second outer frame 31 serving as a lightoutgoing side outer frame that is detachably fixed to the light outgoingside of the intermediate frame 30, a first outer frame 32 serving as alight incident side outer frame that is detachably fixed to the lightincident side of the intermediate frame 30, and a spacer 33 arrangedbetween the liquid crystal modulation element 925R and the transparentplate 963R. The liquid crystal modulation element 925R and thetransparent plate 963R are held between the intermediate frame 30 andthe second outer frame 31, and the transparent plate 962R is heldbetween the intermediate frame 30 and the first outer frame 32.

[0137] The liquid crystal modulation element 925R has a lower stepsurface 9254R at its end portion of the light incident surface. Aflexible cable 9253R for wiring extends from above the liquid crystalmodulation element 925R.

[0138] The intermediate frame 30 is a rectangular frame, and has a lowerstep surface 303 at its inside edge portion on the light outgoingsurface side of the frame portion. The step surface 9254R of the liquidcrystal modulation element 925R is in contact with a surface 302 on thelight outgoing side of the frame portion, and an edge portion of thehigher light outgoing surface of the liquid crystal modulation element925R is in contact with the step surface 303 that is formed on theintermediate frame 30. That is, contact surfaces 302 and 303 for thelight incident surface that are in contact with a part of the lightoutgoing surface of the liquid crystal modulation element 925R areformed on the light outgoing side of the intermediate frame 30.

[0139] In addition, a pair of length-side wall portions 304 extendingalong the length-side side surfaces of the liquid crystal modulationelement 925R and a pair of width-side wall portions 305 extending alongthe width-side side surfaces of the liquid crystal modulation element925R are formed on the outer end of the frame portion of theintermediate frame 30. The length-side wall portions 304 extend to thepositions where the leading ends thereof are equal to the light outgoingsurface of the liquid crystal modulation element 925R. These length-sidewall portions 304 are opposed to the length-side side surfaces of theliquid crystal modulation element 925R at a predetermined distance.

[0140] The leading ends of the width-side wall portions 305 extend tothe width-side side surfaces of the transparent plate 936R across thewidth-side side surfaces of the liquid crystal modulation element 925R.A contact surface 306 for the light valve side surface contacting thewidth-side side surface of the liquid crystal modulation element 925R,and a contact surface 307 for the transparent plate side surfacecontacting the width-side side surfaces of the transparent 963R areformed on the width-side wall portions 305. In this embodiment, thecontact surface 306 for the light valve side surface and the contactsurface 307 for use in the transparent plate side surface are formed onthe same plane.

[0141] The spacer 33 is a rectangular frame having a constant thickness.The lengthwise size of the spacer 33 is set substantially equal to thatof the liquid crystal modulation element 925R, and the width-side sidesurfaces of the spacer 33 are in contact with the contact surface 307for the transparent plate side surface (the contact surface 306 for thelight valve side surface). Projections 331 extending towards the lightincident side are formed on the length-side frame portions of the spacer33. The projections 331 are inserted between the length-side sidesurfaces of the liquid crystal modulation element 925R and thelength-side wall portions 304 formed on the intermediate frame 30.

[0142] In addition, projections 332 extending towards the light outgoingside are formed on the length-side frame portion of the spacer 33. Thetransparent plate 963R is held by the projections 332 from the verticaldirection (the Y direction).

[0143] The second outer frame 31 is a rectangular frame having theconstant thickness thinner than the spacer 33. The overall surface ofthe light incident side of the frame portion of the outer frame 31 is apressure surface 311 for pressing the light outgoing surface of thetransparent plate 963R towards the intermediate frame 30. In addition,the second outer frame 31 has engaging pawls 312 formed on four cornersthereof that extend along the side surfaces of the width-side frameportion of the intermediate frame 30. In contrast, the intermediateframe 30 has engaging projections 341 formed at the positionscorresponding to the engaging pawls 312 that can engage with theengaging pawls 312.

[0144] A procedure of assembling the liquid crystal modulation element925R, the spacer 33, the transparent plate 963R and the second outerframe 31 onto the intermediate frame 30 will now be described.

[0145] First, the liquid crystal modulation element 925R is insertedbetween a pair of width-side wall portions 305 formed on theintermediate frame 30. At this time, the liquid crystal modulationelement 925R is inserted so that the edge portion of the light incidentsurface of the liquid crystal modulation element 925R abuts against thestep surface (light incident-side contact surface) 303 of theintermediate frame 30. This allows the liquid crystal modulation element925R to be arranged at a predetermined position on the intermediateframe 30 by the contact surfaces 302 and 303 for the light incidentsurface and the contact surface 306 for the light valve side surfaces.In this state, as shown in FIG. 13(A), the width-side wall portions 305extend towards the light outgoing side across the width-side sidesurfaces of the liquid crystal modulation element 925R. On the otherhand, as shown in FIG. 13(B), the leading ends of the length-side wallportions 304 and the light outgoing surface of the liquid crystalmodulation element 925R are positioned on substantially the same plane.In this state, the liquid crystal modulation element 925R is notcompletely fixed to the intermediate frame 30, and can be easilyremoved.

[0146] Next, the spacer 33 is superposed on the light incident surfaceof the liquid crystal modulation element 925R along the width-side wallportions 305 of the intermediate frame 30. At this time, if theprojections 331 formed on the spacer 33 are to be inserted between thelength-side side surfaces of the liquid crystal modulation element 925Rand the length-side wall portions 304 of the intermediate frame 30, thespacer 33 is arranged at a predetermined position on the light outgoingsurface of the liquid crystal modulation element 925R.

[0147] Then, the transparent plate 963R is superposed on the spacer 33along the width-side wall portions 305 of the intermediate frame 30. Atthis time, if the transparent plate 963R is to be positioned between theprojections 332 formed on the spacer 33, the transparent plate 963R isarranged on a predetermined position, so that the alignment of theintermediate frame 30, the liquid crystal modulation element 925R, thespacer 33 and the transparent plate 963R in relation to one another isdefined. When the transparent plate 963R is merely superposed on thespacer 33, they are not completely fixed to the intermediate frame 30,and can be removed at any time.

[0148] After that, the second outer frame 31 is attached to theintermediate frame 30 in such a manner that the engaging pawls 312formed on the second outer frame 31 engage with the engaging projections341 formed on the intermediate frame 30. This allows the light outgoingsurface of the transparent plate 963R to be pressed towards theintermediate frame 30 by the pressure surface 311 of the second outerframe 31, so that all of the transparent plate 963R, spacer 33 andliquid crystal modulation element 925R are pressed from the lightoutgoing side onto the intermediate frame 30. Consequently, the liquidcrystal modulation element 925R, the spacer 33 and the transparent plate963R are held between the intermediate frame 30 and the second outerframe 31, and the alignment relation thereof is maintained.

[0149] The structure of the light incident side of the intermediateframe 30 will now be described. The intermediate frame 30 includes awall portion 308 extending along the side surfaces on the periphery ofthe transparent plate 962R on the light incident side thereof, and acontact surface 309 for the light outgoing surface that is in contactwith the edge portion of the light outgoing surface of the transparentplate 962R. A contact surface 310 for the transparent plate side surfacethat is in contact with the side surface of the transparent plate 962Ris formed on the wall portion 309.

[0150] The first outer frame 32 is of an identical shape with the outerframe 31 on the light incident side. That is, the first outer frame 32is a rectangular frame having a constant thickness thinner than thespacer 33. The overall surface on the light outgoing side of the frameportion of the first outer frame 32 is a pressure surface 321 forpressing the light incident surface of the transparent plate 962R to theintermediate frame 30. In addition, the first outer frame 31 hasengaging pawls 322 formed on four corners thereof that extend in thethickness direction of the width-side frame portion of the intermediateframe 30. In contrast, the intermediate frame 30 has engagingprojections 342 formed at the positions corresponding to the engagingpawls 322 that can engage with the engaging pawls 322.

[0151] Therefore, when the transparent plate 962R is fitted to a portionenclosed by the wall portion 308 formed on the intermediate frame 30,the edge portion of the light incident surface of the transparent plate962R strikes the contact surface 309 for the light outgoing surface ofthe intermediate frame 30. In addition, the peripheral side surfaces ofthe transparent plate 962R abut against the contact surface 309 for thetransparent plate side surface formed on the wall portion 308. Thisallows the transparent plate 962R to be arranged at a predeterminedposition on the intermediate frame 30, and a space from the lightincident surface of the liquid crystal modulation element 925R ismaintained. In this state, the transparent plate 962R is not completelyfixed to the intermediate frame 30, and can be easily removed.

[0152] In this state, when the first outer frame 31 is fitted to theintermediate frame 30 so that the engaging pawls 322 formed on the firstouter frame 32 engage with the engaging projections 342 formed on theintermediate frame 30, the transparent plate 962R is pressed by thepressure surface 321 of the first outer frame 32, and the transparentplate 962R is held between the intermediate frame 30 and the first outerframe 32. In addition, the space between the light incident surface ofthe liquid crystal modulation element 925R and the transparent plate 962is shielded from the outside by the wall portion 308 formed on theintermediate frame 30.

[0153] When the liquid crystal modulation element 925R, and thetransparent plates 962R and 963R are held by such a dust-preventingmember 1965R, operability of rework such as replacement of componentscan be improved. That is, if the liquid crystal modulation element 925Rand the transparent plates 962R and 963R are fixed to the intermediateframe 30 with an adhesion or the like, a step for cleaning the adhesiveadhering to the components (the liquid crystal modulation element 925Rand the transparent plates 962R and 963R) is required in the case ofreplacement thereof after separating them from the intermediate frame30. However, if the above dust-preventing member 1965R is used,components can be easily replaced because the components such as theliquid crystal modulation element 925R and the like can be easilyremoved by removing the second outer frame 31 and first outer frame 32at the time of replacement of components.

[0154] In the state where the liquid crystal modulation element 925R isarranged on the intermediate frame 30, while the leading ends of thelength-side wall portions 304 formed on the intermediate frame 30 andthe light outgoing surface of the liquid crystal modulation element 925Rare positioned on substantially the same plane, the width-side wallportions 305 extend to the light outgoing side across the light outgoingsurface of the liquid crystal modulation element 925R, as shown in FIGS.13(A) and (B). Therefore, a roller 40 is put on the light outgoingsurface of the liquid crystal modulation element 925R, and the roller 40can be moved in one direction (the Y direction) by using the transparentplate-side contact surfaces 307 formed on the width-side wall portion305 as guide surfaces.

[0155] An antireflection film (AR film) may be bonded to the lightoutgoing surface of the liquid crystal modulation element for thepurpose of improving the light utilizing use efficiency. In this case,the AR film is placed on the light outgoing surface of the liquidcrystal modulation element 925R and the roller 40 is moved in onedirection as described above, whereby the AR film can be easily bondedto the light outgoing surface. In addition, since the roller 40 can bemoved in one direction, the roller 40 can be easily moved, and airbubbles generated between the light outgoing surface and the AR film canbe effectively eliminated.

[0156] Furthermore, when replacing the AR film to which dust is adhered,first, the second outer frame 31 is removed from the intermediate frame30, and the transparent plate 963R and the spacer 33 are removed fromthe intermediate frame 30. After that, the AR film to which dust isadhered is separated from the light outgoing surface of the liquidcrystal modulation element 925R and a new AR film is bonded with theabove-described procedure. After the renewal of the AR film, the spacer33 and the transparent plate 963R are superposed on the liquid crystalmodulation element 925R, and the second outer frame 31 is fixed to theintermediate frame 30. This allows a renewal operation of the AR film tobe completed. By using the intermediate frame 30 including the guidesurfaces (the contact surface for the transparent plate 307, in thisembodiment), the renewal operation of the AR film to the light outgoingsurface of the liquid crystal modulation element 925 can be also easilyperformed.

[0157]FIG. 14 illustrates the engagement between the engaging pawls 312and 322 and the engaging projections 341 and 342. As shown in thisdrawing, the engaging pawls 312 and 322 formed on the outer frames 31and 32 have rectangular openings 313 and 323, respectively. Engagingprojections 341 and 342 corresponding to the engaging pawls 312 and 322are formed so that they are engaged with the rectangular openings 313and 323 of the engaging pawls 312 and 322, and are located at positionsshifted in the direction perpendicular (the X direction) to thethickness direction (the Z direction) of the intermediate frame 30.

[0158] Since it is difficult to form the intermediate frame on which thepositions of match in the thickness direction of the respective engagingprojections 341 and 342 using upper and lower frames, the engagingprojections to be formed on the intermediate frame should be shifted inthe direction perpendicular to the thickness direction using the firstand second outer frames having different shapes. However, if anengagement mechanism in this embodiment is adopted, the intermediateframe can be easily formed and at the same time, commonality ofcomponents can be achieved by forming the first outer frame 32 and thesecond outer frame 31 into the same shape.

[0159] The structure for attaching the dust-preventing member 1965R tothe light incident surface 911R of the color synthesizing prism 910 isthe same as that of the aforementioned dust-preventing member 965R. Thatis, as shown in FIG. 15, the dust-preventing member 1965R is fixed tothe fixed frame plate 54 that is fixedly bonded to the light incidentsurface 911R of the color synthesizing prism 910. In addition, since theprocedures of attaching the dust-preventing member 1965R to the colorsynthesizing prism 910 using the intermediate frame plate 55 and thefixed frame plate 54, and actions and effects thereof are the same asthose of the dust-preventing member 965R, a description thereof will beomitted.

[0160] <Embodiment 2>

[0161] While the projection display device using a transmissive liquidcrystal modulation element as the liquid crystal modulation element hasbeen described in the embodiment 1, the present invention can be appliedto a projection display device that uses a reflective liquid crystalmodulation element as the liquid crystal modulation element. An exampleof a projection display device to which a reflective liquid crystalmodulation element is adopted will be shown below.

[0162]FIG. 16 is a schematic structural view of the surroundings oflight valves in the projection display device of this embodiment. InFIG. 16, the projection display device includes a blue reflectingdichroic mirror 2941 and a red reflecting dichroic mirror 2942 thatreflect illumination light emitted from a light source lamp unit 8. Ablue light flux B contained in a light flux W is reflected at rightangles by the blue reflecting dichroic mirror 2941 and then, is furtherreflected at right angles by a reflecting mirror 2971, and is incidenton a first polarization beam splitter 2900B provided adjacent to adichroic prism 2910.

[0163] This polarization beam splitter 2900B is formed of a prism havingan s-polarized light flux-reflecting plane 2901B that is formed of apolarized light separation film for reflecting an s-polarized light fluxand transmitting a p-polarized light flux. The polarization beamsplitter 2900B bends an s-polarized light component of the blue lightflux into 90° by the s-polarized light flux-reflecting plane 2901B, andallows the s-polarized light component to be incident on a lightincident and outgoing surface of a reflective liquid crystal modulationelement 2925B that is opposing one side of the polarization beamsplitter 2900B.

[0164] Then, only a p-polarized light of the blue light flux, which ismodulated by the liquid crystal modulation element 2925B and transmittedthrough the s-polarized light flux-reflecting plane 2901B, is emittedfrom the same light incident and outgoing surface to the dichroic prism2910. Incidentally, a transparent plate 2963B is arranged on the side ofthe light incident and outgoing surface of the liquid crystal modulationelement 2925B through a dust-preventing member 2965B.

[0165] On the other hand, a red light flux R and a green light flux Gare first reflected at right angles by the red-green reflecting dichroicmirror 2942, and then further reflected at right angles by a reflectingmirror 2972.

[0166] After being transmitted through a green reflecting dichroicmirror 2941, the red light flux R is incident on a second polarizationbeam splitter 2900R that is provided on an opposite side to the firstpolarization beam splitter 2900B across the dichroic prism 2910. Thesecond polarization beam splitter 2900R is formed of a prism having ans-polarized light flux-reflecting plane 2901R that is formed of apolarized light separation film for reflecting an s-polarized light fluxand transmitting a p-polarized light flux.

[0167] The second polarization beam splitter 2900R bends an s-polarizedlight component of the red light flux into 90° by the s-polarized lightflux-reflecting plane 2901B, and allows the s-polarized light componentto be incident on a light incident and outgoing surface of a reflectiveliquid crystal modulation element 2925R that is opposing one side of thepolarization beam splitter 2900R.

[0168] Then, only p-polarized light of the red light flux, which ismodulated by the liquid crystal modulation element 2925R and transmittedthrough the s-polarized light flux-reflecting plane 2901R, is emittedfrom the same light incident and outgoing surface to the dichroic prism2910. Incidentally, a transparent plate 2963R is arranged on the lightincident side and outgoing surface side of the liquid crystal modulationelement 2925R through a dust-preventing member 2965R.

[0169] After being reflected by a green reflecting dichroic mirror 2943,the green light flux G is incident on a third polarization beam splitter2900G that is provided on one side of the dichroic prism 2910. The thirdpolarization beam splitter 2900G is formed of a prism having ans-polarized light flux-reflecting plane 2901G that is formed of apolarized light separation film for reflecting an s-polarized light fluxand transmitting a p-polarized light flux. This polarization beamsplitter 2900G bends an spolarized light component of the green lightflux into 90° by the s-polarized light flux-reflecting plane 2901G, andallows the s-polarized light component to be incident on a lightincident and outgoing surface of a reflective liquid crystal modulationelement 2925G that is opposing one side of the polarization beamsplitter 2900G.

[0170] Then, only p-polarized light of the green light flux, which ismodulated by the liquid crystal modulation element 2925G and transmittedthrough the s-polarized light flux-reflecting plane 2901G, is emittedfrom the same light incident and outgoing surface to the dichroic prism2910. Incidentally, a transparent plate 2963G is arranged on the lightincident side and outgoing surface side of the liquid crystal modulationelement 2925G through a dust-preventing member 2965G.

[0171] As described above, the light fluxes B, R and G modulated throughthe respective liquid crystal modulation elements 2925B, 2925R and 2925Gare incident on the dichroic prism 2910, where they are synthesized. Thesynthesized color image is enlarged and projected through a projectionlens unit 6 onto a screen that is placed at a predetermined position.

[0172] In such a projection display device using the reflective liquidcrystal modulations 2925R, 2925G and 2925B, since light outgoingsurfaces of the reflective liquid crystal modulation elements 2925R,2925G and 2925B are protected by the transparent plates 2963R, 2963G and2963B, the heat generated by the outgoing-side polarizers 961R, 961G and961B can be prevented from being transmitted to the liquid crystalmodulation elements 925R, 925G and 925B. This makes it possible torestrict the increase in temperature of the liquid crystal modulationelements 925R, 925G and 925B and to prevent the deterioration of theoptical properties thereof.

[0173] In addition, since the liquid crystal modulation elements 925R,925G and 925B and the outgoing-side polarizers 961R, 961G and 961B areapart from each other, the light emitted from the liquid crystalmodulation elements 925R, 925G and 925B widely spread, and thepolarizers 961R, 961G and 961B can receive the light in a wide area. Forthis reason, it is possible to decrease the heat generated by thepolarizers 961R, 961G and 961B per unit area, and to permit easy heatdissipation. In particular, it is effective to arrange a microlensarray, which gathers light onto each pixel of the liquid crystalmodulation element, on the light incident surface of the liquid crystalmodulation elements 925R, 925G and 925B because the light can spreadmore widely.

[0174] Furthermore, the surfaces of such transparent plates 2963R, 2963Gand 2963B may be coated with a surface-active agent (surfactant), ortreated for electrostatic protection. Since this makes it difficult fordust to adhere to the surfaces of the transparent plates 2963R, 2963Gand 2963B, the adhesion of dust can be prevented more effectively.

[0175] <Other Embodiments>

[0176] While the projection display device having three liquid crystalmodulation elements for modulating three color lights, respectively, isdescribed in the above embodiments, a projection display device to whichthe present invention is applied is not limited to the above-describeddevice, for example, it may use only a single liquid crystal modulationelement. In addition, the projection display devices are divided intotwo types, a front type that performs projection from the side on whichthe screen is observed, and a rear type that performs projection fromthe side opposite to the screen observing side, and the presentinvention is applicable to either of the types.

INDUSTRIAL APPLICABILITY

[0177] The present invention can be utilized as a projection displaydevice that optically processes a light flux emitted from a light sourceand enlarges and projects an image onto a projection plane, such as avideo projector having liquid crystal modulation elements.

1. An optical modulation element for modulating a light flux emittedfrom a light source according to image information, wherein atransparent plate is provided on at least one surface thereof, and thespace between the transparent plate and said optical modulation elementis shielded from the outside by a dust-preventing member.
 2. The opticalmodulation element according to claim 1 , wherein said dust-preventingmember is formed of resin containing glass fiber.
 3. The opticalmodulation element according to claim 1 , wherein said dust-preventingmember is made of metal.
 4. The optical modulation element according toclaims 1 to 3 , wherein a polarizer is bonded to said transparent plate.5. The optical modulation element according to claims 1 to 3 , whereinat least one surface of said transparent plate is coated with asurface-active agent, or treated for electrostatic protection.
 6. Aprojection display device having an optical modulation element formodulating a light flux emitted from a light source according to imageinformation, and projection means for enlarging and projecting the lightmodulated by said optical modulation element onto a projection plane,wherein a transparent plate is provided on the side of a light outgoingsurface of said optical modulation element, and a space between saidtransparent plate and the light outgoing surface of said opticalmodulation element is shielded from the outside by a dust-preventingmember.
 7. The projection display device according to claim 6 , whereinsaid dust-preventing member has a frame body for holding said opticalmodulation element, said transparent plate and said spacer, and a lightoutgoing-side outer frame detachably fixed to the light outgoing side ofsaid frame body, said frame body includes a contact surface for thelight incident surface contacting a part of the light incident surfaceof said optical modulation element, a contact surface for the opticalmodulation element side surface contacting the side surface of saidoptical modulation element and a contact surface for the transparentplate side surface contacting the side surface of said transparentplate, and said light outgoing-side outer frame includes a pressuresurface that can press a part of the light outgoing surface of saidtransparent plate towards said frame body.
 8. The projection displaydevice according to claim 7 , wherein said frame body has a guidesurface formed thereon for putting a roller on the light outgoingsurface of said optical modulation element and moving said roller in onedirection.
 9. The projection display device according to any one ofclaims 6 to 8 , wherein an antireflection film is provided on thesurface of said transparent plate.
 10. The projection display deviceaccording to any one of claims 6 to 9 , wherein said optical modulationelement is the transmissive optical modulation element, and a lightincident-side transparent plate is provided on the side of the lightincident surface of said transmissive optical modulation element. 11.The projection display device according to claim 10 , wherein a spacebetween said light incident-side transparent plate and the lightincident surface of said transmissive optical modulation element is cutoff from the outside by said dust-preventing member.
 12. The projectiondisplay device according to claim 11 , including a light incident-sideouter frame to be detachably fixed to the light incident side of saidframe body, wherein said light incident-side outer frame includes apressure surface that can press a part of the light incident surface ofsaid light incident-side transparent plate towards said frame body, andsaid frame body includes a contact surface for the light outgoingsurface contacting a part of the light outgoing surface of said lightincident-side transparent plate, and a contact surface for thetransparent plate contacting the side surface of said lightincident-side transparent plate.
 13. The projection display deviceaccording to claim 12 , wherein said light incident-side outer frame andsaid light outgoing-side outer frame are formed into the same shape andinclude engaging pawls extending along side surface of said frame body,said frame body includes engaging projections corresponding to saidengaging pawls, respectively, and the respective engaging projectionsare formed at the positions shifted in a direction perpendicular to thethickness direction of said frame body.
 14. The optical modulationelement according to claim 6 , wherein said dust-preventing member isformed of resin containing glass fiber.
 15. The optical modulationelement according to claim 6 , wherein said dust-preventing member ismade of metal.
 16. The optical modulation element according to claims 6to 13 , wherein a polarizer is bonded to said transparent plate.
 17. Theoptical modulation element according to claims 6 to 13 , wherein atleast one surface of said transparent plate is coated with asurface-active agent, or treated for electrostatic protection.
 18. Aprojection display device for separating a light flux emitted from alight source into a plurality of color light fluxes, modulating thecolor light fluxes according to image information through an opticalmodulation element, synthesizing the color light fluxes modulated bysaid optical modulation element by color synthesizing means, andenlarging and projecting light synthesized by said color synthesizingmeans onto a projection surface through projection means, saidprojection display device including: a transparent plate provided on theside of a light outgoing surface of said optical modulation element, adust-preventing member for holding said transparent plate and saidoptical modulation element, and shielding the space between saidtransparent plate and the light outgoing surface of said opticalmodulation element from the outside, a fixed frame plate fixed on thelight incident surface of said color synthesizing means, and anintermediate frame plate removably fixed to said fixed frame plate,wherein said dust-preventing member is fixed to said intermediate frameplate.
 19. The projection display device according to claim 18 includingpositioning means for positioning said optical modulation element bydefining the mounting position of said dust-preventing member.
 20. Theprojection display device according to claim 18 , wherein said opticalmodulation element is the transmissive optical modulation element, saidtransparent plate is also provided on the side of the light incidentsurface of said transmissive optical modulation element, saidtransparent plate is also held by said dust-preventing member, and thespace between said transparent plate and the light incident surface ofsaid transparent plate optical modulation element is shielded from theoutside by said dust-preventing member.
 21. The projection displaydevice according to claims 18 to 20 , wherein a polarizer is provided onsaid light incident surface of said color synthesizing means, and thebonded surface of said fixed frame plate to said light incident surfaceis not completely covered with said polarizer.
 22. The projectiondisplay device according to claims 18 to 21 , wherein at least onesurface of said transparent plate is coated with a surface-active agent,or treated for electrostatic protection.
 23. The projection displaydevice according to claims 18 to 21 , wherein a polarizer is bonded tosaid transparent plate.
 24. The projection display device according toclaims 18 to 23 , wherein said dust-preventing member is formed of resincontaining glass fiber.
 25. The projection display device according toclaims 18 to 23 , wherein said dust-preventing member is made of metal.